For a Category I natural draft gas appliance with an input rating of 125,000 Btu/h, what is the appropriate size vent required for a height of 15 feet and a 2-foot lateral?

To determine the appropriate size vent for a Category I natural draft gas appliance, a few important factors must be taken into account, including the appliance's input rating, venting height, and the presence of lateral distances.

Given that the appliance has an input rating of 125,000 Btu/h, we must follow a vent sizing chart or guidelines typically used for gas appliances. For natural draft appliances, vent size increases with both the BTU input and the height of the vent. The vent's diameter is critical in ensuring proper draft and exhaust of combustion gases.

In this case, a height of 15 feet and a lateral distance of 2 feet positively influence the vent sizing. The height aids in the vent's ability to create adequate draft due to the natural rise of hot gases. Additionally, the lateral run contributes to the total resistance against the flow of gases, which also impacts the size needed.

After referencing standard sizing tables for natural draft gas appliances, a vent size of 5 inches in diameter is indeed appropriate for an input rating of 125,000 Btu/h, particularly with the specified height and lateral. This choice ensures that the appliance can operate safely and efficiently by facilitating optimal venting of flue gases while maintaining adequate draft